train_test_split: test_size default is None
If test_size is None and train_size is not None, test_size
is the complement of train_size. If test_size and train_size
are None, test_size = 0.25.
Docstring is updated.
Existing tests didn't seem to cover much of existing behaviour
and no updates were added. New behaviour was tested.
Modified docstrings
Modified docstrings and tests
DOC updated whatsnew